1. Technical Field
The present technology pertains generally to fluid stream separation schemes and methods for producing metal-organic frameworks, and more particularly to the production and use of metal-organic frameworks with metal atoms that are coordinatively bound to polytopic linkers and ligands that expose basic nitrogen atoms to the pore volumes and the flow of gases.
2. Background
Carbon dioxide generated from the combustion of fossil fuels for heat and electricity production is a major contributor to climate change and ocean acidification. The predicted growth of the global economy and world population in the near future will lead to an increased demand for energy, resulting in even further increases in the concentration of CO2 in the atmosphere. In 2012, coal and natural gas fired power plants released more than 11.1 gigatons of carbon dioxide in to the atmosphere, which accounts for nearly 30% of total global emissions.
To mitigate the effects of rising atmospheric CO2 levels related to the burning of fossil fuels, various strategies are used to control and capture CO2 emissions. However, there few financial incentives to reduce CO2 emissions in many countries and existing carbon capture technologies are simply too expensive to be practical at the scales required for large power plants that can release several tons of CO2 per minute. The most expensive component of any carbon capture and sequestration process is usually the separation of CO2 from the other gases that are present in the flue gas of a power plant. There is a need for the development of new materials and processes to remove CO2 from flue gas using as little energy and cost as possible.
While the exact composition of a flue gas depends on the design of the power plant and the source of natural gas or coal, a mixture of mostly N2, CO2, and H2O is present along with potentially more reactive gases that are in lower concentrations, such as O2, SOx, NOx, and CO. Typical flue gas is also released at ambient pressure and at temperatures ranging from about 40° C. to 80° C.
The separation of CO2 from H2 is also important in the context of two distinct applications: (i) the capture of pre and post combustion CO2 emissions like those produced from coal gasification power plants, and (ii) the purification of hydrogen gas, which is synthesized on large scales annually. Separation of CO2 from CH4 is another separation relevant to the purification of natural gas, which can have up to 92% CO2 impurity at its source. Carbon dioxide removal is required for approximately 25% of the natural gas reserves in the United States. Removal of CO2, is typically conducted at pressures between 20 bar and 70 bar with existing processes.
The removal of CO2 from low-pressure flue gas mixtures and other CO2 gas separations is generally performed with aqueous amine solutions that are selective for acid gases. Amines are known to be very selective toward CO2 capture from flue gases or feedstock gases because of the strong chemical bonds formed in the chemisorption process. However, the use of these liquid materials has a number of drawbacks. Regeneration of such absorbents is only possible at high temperatures and the system therefore requires a high input of energy. In addition, corrosion inhibitors need to be used with aqueous amine materials increasing cost, and amine vapors can contaminate the gas streams that are being treated.
As a result of the large energy penalty for desorbing CO2 from such liquid absorbents, solid adsorbents with significantly lower heat capacities are frequently proposed as promising alternatives. Advanced solid adsorbents also have the potential to decrease significantly the cost of CO2 removal from the effluent streams of fossil fuel-burning power plants.
Solid adsorbents, including zeolites, activated carbons, silicas, and metal-organic frameworks, have received significant attention as alternatives to amine solutions, demonstrating high CO2 capacities and high selectivities for CO2 over N2, together with reduced regeneration energy penalties. For example, zeolites have attracted attention as solid adsorbents for carbon dioxide capture. Compared to aqueous alkanolamine absorbents, zeolites require significantly less energy input for adsorbent regeneration. However, zeolites have hydrophilic properties that limit their application to separations that do not include water.
Activated carbon is another solid adsorbent for carbon dioxide separations that requires less energy for regeneration and its hydrophobic properties lead to better performance under moisture conditions compared to zeolites. While the high surface area of activated carbon contributes to much higher carbon dioxide capture capacities at high pressures, it does not perform very well at low pressure ranges.
Metal organic frameworks, (MOFs), an emerging class of nanoporous crystalline solids built of metal coordination sites linked by organic molecules, show promising properties for gas capture applications. Due to their high surface areas and tunable pore chemistry, the separation capabilities of certain metal-organic frameworks have been shown to meet or exceed those achievable by zeolite or carbon adsorbents.
Although metal organic framework materials offer well-defined porosity, high surface area, and tunable chemical functionalities, many materials have hydrophilic properties that limit their application since it is observed that the CO2 uptake capacity dramatically decreases in humid conditions.
Accordingly, there is a need for efficient methods and materials for selectively separating constituent gases from a stream of gases that can be performed at lower temperatures and pressures and regeneration energies than existing techniques. There is also a need for materials and methods that provide effective separations at low cost. The present invention satisfies these needs as well as others and is generally an improvement over the art.